Rails 3.如何從查詢結果中刪除重複的關聯記錄？

我有@invoices，其中包含與特定預定課程有關的所有發票。Rails 3.如何從查詢結果中刪除重複的關聯記錄？

scheduled_course has_many :invoices, through => :enrollments 
invoices belongs_to :scheduled_courses 

@scheduled_course = ScheduledCourse.find(params[:id]) 
@invoices = @scheduled_course.invoices

現在，一些發票可能會被複制。例如，@invoices - @scheduled_course.invoices可能輸出...

=> [#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2bcc9c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b828c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7e54,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7a1c,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, 
#<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b75e4,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">, #<Invoice id: 85, company_id: 106, invoice_number: "2870", issued_on: "2012-03-27", status: "pagado", notes: "", created_at: "2012-05-02 15:28:13", updated_at: "2012-05-02 15:50:50", exchange_rate: #<BigDecimal:c2b7198,'0.12E2',4(8)>, student_id: nil, due_date: "2012-04-02">

如何從結果中移除重複的對象？

來源

2012-06-07 leonel

你就不能打電話uniq呢？ – Sean

使用uniq會將查詢轉換爲數組，這可能會對性能產生負面影響。 – yagooar

您可以通過:uniq選項有很多：

has_many :invoices, :through => :enrollments, :uniq => true

下面是RoR的文檔此選項的說明：

如果爲真，重複將從收集被省略。與...一起使用。

此外，爲了避免在第一時間進入DB副本，您可以使用一個獨特的數據庫索引，這可能是這個樣子：

add_index :enrollments, [:invoice_id, :scheduled_course_id], :unique => true

來源

2012-06-07 19:06:29

我喜歡這個解決方案。 – Kyle

該解決方案將在Rails 4.0中被棄用，甚至可能在Rails 4.1中不存在，所以鼓勵使用替代lambda版本：has_many：invoices， - > {＃get unique elements}，：through =>：enrollments – yagooar

@scheduled_course.invoices.uniq(&:id) # uniq elements in the array by their id

只使用@scheduled_course.invoices.uniq也應該工作。

來源

2012-06-07 19:00:49 Kyle

請記住，#uniq會將ActiveRecord關聯轉換爲發票數組，這會對獲取元素所需的性能和時間產生負面影響。 – yagooar

是的，使用'distinct'代替。 –

Rails 3.如何從查詢結果中刪除重複的關聯記錄？

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